Based on the fuzzy local information c-means （FLICM） clustering algorithm, a new method is developed for extracting the equatorward and poleward boundaries of the auroral oval from images acquired by the Ultraviolet...Based on the fuzzy local information c-means （FLICM） clustering algorithm, a new method is developed for extracting the equatorward and poleward boundaries of the auroral oval from images acquired by the Ultraviolet Imager （UVI） aboard the POLAR satellite. First, the method iteratively segments the UVI image with the FLICM clustering algorithm, according to an integrity criterion for the segmented auroral oval. Then, possible gaps in the extracted auroral oval are filled, based on prior knowledge of its shape. To evaluate the method objectively, the extracted boundaries are compared with the precipitating electron boundaries determined from DMSP satellite precipitation particle data. The evaluation results demonstrate that the proposed method generates more accurate auroral boundaries than traditional methods.展开更多
Using high temporal resolution optical data obtained from three-wavelength all-sky imagers at Chinese Yellow River Station in the Arctic, together with the EISCAT Svalbard radar （ESR） and SuperDARN radars, we invest...Using high temporal resolution optical data obtained from three-wavelength all-sky imagers at Chinese Yellow River Station in the Arctic, together with the EISCAT Svalbard radar （ESR） and SuperDARN radars, we investigated the dayside pole- ward moving auroral forms （PMAFs） and the associated plasma features in the polar ionosphere under difibrent interplanetary magnetic field （1MF） conditions, between 0900 and 1010 UT on 22 December 2003. Simultaneous optical and ESR observations revealed that all PMAFs were clearly associated with pulsed particle precipitations. During northward IMF, particles can precipi- tate into lower altitudes and reach the ionospheric E-region, and there is a reverse convection cell associated with these PMAFs. This cell is one of the typical signatures of the dayside high-latitude （lobe） reconnection in the polar ionosphere. These results indicate that the PMAFs were associated with the high-latitude reconnection. During southward IMF, the PMAFs show larger lati- tudinal motion, indicating a longer mean lifetime, and the associated ionospheric features indicate that the PMAFs were generated by the dayside low-latitude reconnection.展开更多
Using high temporal resolution optical data obtained from three-wavelength all-sky imagers over six winters continuously at Yellow River Station (78.92°N,11.93°E) in Arctic,we statistically investigated the ...Using high temporal resolution optical data obtained from three-wavelength all-sky imagers over six winters continuously at Yellow River Station (78.92°N,11.93°E) in Arctic,we statistically investigated the dependence of location of poleward moving auroral forms (PMAFs) on the interplanetary magnetic field (IMF) B z and B y components as a function of MLT and MLAT under stable IMF conditions.It is found that more PMAFs occurred in lower latitude for Bz<0 and there was less evident IMF B y-related prenoon-postnoon asymmetry for Bz<0 than for Bz>0.We found that the PMAFs were distributed over a wide range of MLT when Bz<0,which indicates that the reconnection X-line might spread like an 'S' shape.However,during northward IMF,PMAFs were observed predominantly prenoon for IMF By>0 and postnoon for IMF By<0 associating with the effect of the high-latitude reconnection,which is largely consistent with the theoretical model of the convection flow.展开更多
基金supported by the National Natural Science Foundation of China (Grant nos.60872154,41031064,40904041,40974103)the National High Technology Research and Development Program of China (Grant no.2008AA121703)the Ocean Public Welfare Scientific Research Project, State Oceanic Administration of China (Grant no.201005017)
文摘Based on the fuzzy local information c-means （FLICM） clustering algorithm, a new method is developed for extracting the equatorward and poleward boundaries of the auroral oval from images acquired by the Ultraviolet Imager （UVI） aboard the POLAR satellite. First, the method iteratively segments the UVI image with the FLICM clustering algorithm, according to an integrity criterion for the segmented auroral oval. Then, possible gaps in the extracted auroral oval are filled, based on prior knowledge of its shape. To evaluate the method objectively, the extracted boundaries are compared with the precipitating electron boundaries determined from DMSP satellite precipitation particle data. The evaluation results demonstrate that the proposed method generates more accurate auroral boundaries than traditional methods.
基金supported by the National Natural Science Foundation of China (Grant nos. 40974083, 41031064, 41104091,41104090, 41274149 and 41274164)the Ocean Public Welfare Scientific Research Project of China (Grant no. 201005017)+1 种基金the Polar Strategic Research Foundation of China (Grant nos. 20100202, 20100203 and 20120304)the Polar Environment Comprehensive Investigation & Assessment Programs(Grant no. CHINARE 2012-02-03)
文摘Using high temporal resolution optical data obtained from three-wavelength all-sky imagers at Chinese Yellow River Station in the Arctic, together with the EISCAT Svalbard radar （ESR） and SuperDARN radars, we investigated the dayside pole- ward moving auroral forms （PMAFs） and the associated plasma features in the polar ionosphere under difibrent interplanetary magnetic field （1MF） conditions, between 0900 and 1010 UT on 22 December 2003. Simultaneous optical and ESR observations revealed that all PMAFs were clearly associated with pulsed particle precipitations. During northward IMF, particles can precipi- tate into lower altitudes and reach the ionospheric E-region, and there is a reverse convection cell associated with these PMAFs. This cell is one of the typical signatures of the dayside high-latitude （lobe） reconnection in the polar ionosphere. These results indicate that the PMAFs were associated with the high-latitude reconnection. During southward IMF, the PMAFs show larger lati- tudinal motion, indicating a longer mean lifetime, and the associated ionospheric features indicate that the PMAFs were generated by the dayside low-latitude reconnection.
基金supported by the National Natural Science Foundation of China (Grant Nos. 41031064,40974103,40974083,40904041,40890164,41104091,and 41104090)the Polar Strategic Research Foundation of China (Grant No. 20120304)the Ocean Public Welfare Scientific Research Project,State Oceanic Administration of the People's Republic of China (Grant No. 201005017)
文摘Using high temporal resolution optical data obtained from three-wavelength all-sky imagers over six winters continuously at Yellow River Station (78.92°N,11.93°E) in Arctic,we statistically investigated the dependence of location of poleward moving auroral forms (PMAFs) on the interplanetary magnetic field (IMF) B z and B y components as a function of MLT and MLAT under stable IMF conditions.It is found that more PMAFs occurred in lower latitude for Bz<0 and there was less evident IMF B y-related prenoon-postnoon asymmetry for Bz<0 than for Bz>0.We found that the PMAFs were distributed over a wide range of MLT when Bz<0,which indicates that the reconnection X-line might spread like an 'S' shape.However,during northward IMF,PMAFs were observed predominantly prenoon for IMF By>0 and postnoon for IMF By<0 associating with the effect of the high-latitude reconnection,which is largely consistent with the theoretical model of the convection flow.
